Will dry yeast do any good when brewing a lager or is it necessary that you use a liquid one? I am talking about making some kind of starter with the yeast, not just pitching it into the fermenter. How much difference in flavor does it make? Do dry yeasts make a descent lagering?

I don't have any experience with dry yeast for lagering. In general you do not need to make a starter with dry yeasts, because you end up pitching too much. Over-pitching is just as bad as under-pitching. I use this pitching rate calculator: mrmalty.com/calc/calc.html
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Dean BrundageFeb 6 '10 at 15:46

2 Answers
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Dried yeast is a perfectly good product to use, and it will yield appropriate flavour characteristics for the type of strain you decide to use. The biggest difference with dried yeast is that it has a lot more trehalose than liquid yeast, about 12-15% of the dried weight. Trehalose is just a disaccharide made up of two glucoses. Its role is to protect the yeast cell from extra cellular stresses, like in this instance dehydration. Many breweries will use dried yeast for specialities because dried yeast has a longer shelf life than the liquid ones. So there is no reason to worry.

You need to be careful though when preparing your yeast for pitching! Make sure that you mix the yeast with sterile water or wort before pitching into your beer. Use 10 times the amount of wort as to the yeast’s dry weight. Try to get the temperature of your wort as close to 100 degrees Fahrenheit (38 degrees Celsius) as possible when mixing the two together. This will improve your yeasts viability and fermentation performance. Rehydration at lower temperatures will hurt your yeasts viability. Mix the wort with the yeast for 5 minutes before pitching it into your lager. I recommended inoculating the slurry into your final beer at 68 degrees Fahrenheit (20 degrees Celsius) for optimum results.

Yeah, 38 C might even kill the yeast. I will stick to the official guidelines and pitch it in a wort at about 25 C, that's what i always do anyway, and the leave it until it reaches 20 degrees to pitch it into the rest of the wort. Since this is not a real starter, just a rehydration, do you think using raw cane sugar is ok or it's better to use malt extract like in starters?
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TetragrammatonFeb 7 '10 at 14:58

Add sugar (any kind is fine) only if you want to "proof" the yeast - see if it starts fermenting. Otherwise, just use sterile water.
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Dean BrundageFeb 7 '10 at 18:06

Just to point it out (and be a biochemistry geek), maltose is also a glucose to glucose dissaccharide. The difference between the trehalose and maltose though is how the two glucose molecules are bonded together...but we'll save that lesson for another day. :)
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brewchezFeb 8 '10 at 13:35

Reading over the comments from my last post I see my previous answer must have been incredibly confusing. Let me try again. The yeast being used is dried. To make it wet and living you need to add clean water or preferably clean wort to it. Wort is the sugar water extracted from your grain. The temperature you should make the yeast wet at should be close to 38 degrees Celsius. If the temperature is any lower than this, your fermentation won’t be as quick or active. For any of you who are interested re-hydration at 38 degrees Celsius will yield 60-70% viability, 20 degrees Celsius 30-40% viability and 4 degrees Celsius 20-25% viability. This is a separate process from adding the yeast to the beer. When you are wetting the yeast with wort or water you are making something called yeast slurry.

Once you have made your yeast slurry. Let it sit for five to ten minutes stirring occasionally. The beer you are making is totally separate. The temperature of your beer can be 20 degrees Celsius, but since this is a lager, it can also be lower than 20. Most lager strains will work happily at 13 degrees Celsius. Once your slurry is mixed you will pour the slurry along with your soon to be beer into whatever you are using for a fermentation vessel. This is called pitching. You are not throwing the bag of yeast directly into the wort and this wort is not at some outrageous temperature. The high temperature is just for making the slurry. This temperature will not kill the yeast it will make it more alive.

Re-hydration temperatures are typically high to improve viability in laboratory procedures. Some published in the Journal of the Institute of Brewing and the Journal of Brewing Science. I don’t really have time to go through and pull out multiple sources to justify my advice. Industrially, high hydration temperatures are used to conserve slurring time and reduce contamination risks. Most these processes have heat exchangers for rapid cooling.
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AdamFeb 9 '10 at 21:55

You did not specify in your query a specific yeast product or size. As you will see the guidelines specified by your provider require up to a half hour of preparation time while I outlined five minutes. I would strongly advise you to follow the directions written on the packet. The lager you will produce will meet quality specification, but your yeast will be more than half dead at the end of the fermentation and I would not advise reusing the product in another brew.
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AdamFeb 9 '10 at 21:55